A structural model of the transmembrane portion of the acetylcholine receptor has been constructed. Sequences of all its subunits were analyzed using partition energy calculations to determine locations and orientations of transmembrane Alpha helices. Side chain packing calculations were used to stack the transmembrane helices together. In the model, each subunit has the following structures in order along the N terminal: a large extracellular domain of undetermined structure, a short apolar Alph helix that lies on the extracellular lipid surface of the membrane, three apolar transmembrane Alpha helices (I, II, and III); a cytoplasmitc domain of lndeterminined structure; an amphipathic transmembrane helix (L) that forms the channel lining; a short extracellular helix; another apolar transmembrane helix (IV) and a small cytoplasmic domain formed by the C terminal of the chain. This model differs from others principally in that the channel lining is comprised of a bundle of five amphipathic L helices. These are surrounded by a bundle of ten alternating II and III helices. Mechanisms for conformational changes that open and close the channel are being studied. Applications to other proteins, both to verify method and to extend the applications are anticipated.